1. Field of the Invention
This invention relates generally to a method and apparatus for cutting thin sheet laminates, and more particularly to a precision die for cutting a cavity pattern in unfired or "green" low temperature cofired ceramic (LTCC) sheets.
2. Description of Related Art
Cavities are known to be formed in laminated multilayer low temperature cofired ceramic (LTCC) structures such as substrates for electronic circuitry, and more particularly integrated circuits to isolate signals and to use the ceramic itself as component housing. Such a structure is shown, for example, in the aforementioned related application, U.S. Ser. No. 08/686,000 (WE58,831).
In order to form these components which often involve complex shapes, the individual sheets of unfired or "green" tape of LTCC material have a cavity pattern cut into them prior to lamination. Individual sheets may typically have anywhere between 10 and 200 cavities of various shapes and sizes formed therein. One part design, for example, may require between 2 and 8 different cavity patterns.
Conventional practice for forming cavities in unfired LTCC laminates currently involves one of four well known methods, namely: mechanical routing, hard-die tooling, laser cutting and punch nibbling. All of these methods require moderate to high capital investment; however, the trade off in these methods is in the volume vs. labor hours required.
With respect to mechanical routing, a capital investment of $70K-$80K would typically be involved and while relatively precise (0.002 in.) cutting can be obtained, a set-up time and run time of 5-10 minutes per layer is normally required, depending upon the complexity of the design. Furthermore, cavity complexity adds considerably to the run time, even though a wide variety of complex designs can be accommodated.
With respect to hard die tooling, a typical capital investment of $40K-$75K dollars per cavity layer design is required. A precision of 0.001-0.002 inches is typical, and a set up and run time of 0.5-1 minute per layer is needed regardless of cavity complexity and can accommodate any design complexity. However, a large-volume fixed design product normally associated with this type of fabrication.
With respect to laser cutting, a relatively high capital investment of $80K-$200K dollars is typically required, and although a relatively precise (&lt;0.002 in.) product can be fabricated, set up and run time of 5-20 minutes per layer is required. Increased complexity adds considerably to run time, even though any complex design can be accommodated. Also, considerable engineering support is normally required for maintaining such apparatus.
As to punch nibbling, a relatively high capital investment $100K-$150K dollars is normally required; however, relatively high precision (&lt;0.001 in.) can be obtained. Since this type of equipment is automated, run times are varied and difficulties with complex designs are encountered due to fixed punch sizes. Such apparatus is also accompanied by considerable engineering support. Also, conductor printing difficulties are encountered, since cavities are formed prior to conductor printing.